A need exists in printing apparatus for a print hammer driving mechanism which can provide optimum hammer speed and variable hammer impact. Variations in the desired amount of hammer impact force may arise for a number of reasons, such as variations in the number of copies to be printed simultaneously; variations in the effective areas of individual characters to be printed, such as, for example, the area of the letter "w" as compared to the area of the letter "v", or the area of the number "8" as compared to the area of the number "1"; the quality of print which may be required for a particular application; and the style or font of a character to be printed.
The desirability of controlling printing intensity has been recognized, for example, in U.S. Pat. No. 3,172,353, in which energy produced by a magnetic field and imparted to a print hammer can be reduced by reducing the amplitude of the current driven through the coil.